Mitsubishi Duel MiniSplit-Humidity

[kool55]

I updated my Barn tack room and feed room [both12x12] over the winter. I installed a Mitsubishi 24,000 btu condenser unit and 2 -6,000 btu wall units. Installed with no issues. Nitrogen pressure checked for 24 hrs. ,no leaks etc.
Heat function worked when it was cold outside and the cooling function is good
Can get both rooms to cool to 63 degrees.
Problem is I have high humidity,85-90%. Very little condensate from the drain lines. Even in Humidity mode. The drain lines are clear with no restrictions. Any ideas? Thanks

 

[SALIV8]

What fan speed are you using?

Id try fan on lowest speed and see if that helps.

 

[kool55]

I have tried all 3 speeds.

 

[PsRumors]

How long are the run cycles? It will need to run quite a while continuously to remove that much humidity.

Are the rooms connected with a door? If so, open the door but only run one unit.

I suspect you have too much cooling capacity

 

[kool55]

The rooms are separated by a solid wall.
One entry door each. No windows. The wall unit fans run for extended periods of time. I know from working on finishing up details in these rooms.
Both rooms are insulated. Concrete floors have vinyl flooring. The addition of the tack room converted from a horse stall, I even put 2'' foam sheets and vapor barrier down before the concrete pour. The rooms have been done for a couple of months.

 

[jjrbus]

I am in Florida with 3 DAikin mini's and have high humidity, usually running over 60%. I do not know what the humidity was with the previous central air as I never checked.

I would bet money that I have properly sized my units, using manual J, the previous unit and a window unit that was used temporarily. But am starting to suspect I have too much capacity as I run all 3 minis most of the time on the night or silent setting.

When I went to clean the first mini installed, the blower fan was caked with mold, which turned into an ordeal to clean. The main suspect for this happening is high humidity. So might want to check your blower fan on the inside unit.

Because the inside fans run all the time it is difficult to tell how often the units are cycling. It is on the bucket list to figure out a way to check cycling. I have put a pan under one mini drain outside to see how much water is being removed and the one I checked is removing water. But how do I know how much is right. Need to research this.

By the way I lived with mini's in Asia and know they are capable of keeping humidity levels down.

 

[Jackfre]

I think your condensing unit is to large for the load you are trying to control. What is the minimum output on the unit? You could try high and low registers cut through the wall and possibly add a fan between them to double the space only one unit is handling.
I have found when sizing mini-splits that how low it goes is more important to your comfort than how big a unit you can buy.

 

[LS6 Tommy]

Your system is completely mismatched. You have double the tonnage needed for the air handlers. You're only running long enough to remove sensible heat and not removing any latent heat, which is what removes moisture.

Tommy

 

[kool55]

That sort of makes sense. I will have to go back on the supplier I got this from. I wanted the smallest evaporators I could get due to the room size.They came up with this combination. I knew the evaporators needed to run for a longer period of time to get the desired effect.
Since this is an inverter system ,the condenser fan is not spinning very fast alluding to what you are telling me.
But on the other hand wouldn't a too large evaporator be more detrimental than a too large condenser?

 

[kool55]

This is from the Mitsubishi Compatibility chart. These are the units .
Condenser , MXZ-2C20NA2
Evaporator, MSZ-GL06NA

 

[MattT]

I have put a pan under one mini drain outside to see how much water is being removed and the one I checked is removing water. But how do I know how much is right. Need to research this.

Was draining one of my 12K units into a 5 gallon bucket last summer. Was collecting 4+ gallons in 24 hours on hotter days. This unit is dead on actual and 1/2 ton undersized by Man J so it's running pretty hard. Haven't measured indoor RH but it feels good.

 

[MattT]

This is from the Mitsubishi Compatibility chart. These are the units .
Condenser , MXZ-2C20NA2
Evaporator, MSZ-GL06NA

Your issue isn't that those heads are incompatible with the condenser. You just don't appear to have enough total load for the 18K nameplate, 5.7K minimum, condenser with only 2 x 6K heads. And I'm guessing those heads aren't seeing anywhere near full load just going by your square footage.

 

[jjrbus]

Was draining one of my 12K units into a 5 gallon bucket last summer. Was collecting 4+ gallons in 24 hours on hotter days. This unit is dead on actual and 1/2 ton undersized by Man J so it's running pretty hard. Haven't measured indoor RH but it feels good.

Just come in from putting a couple pans under drains to see what is happening. Did a quick google and all I found was from 5 to 20 gallons a day for central air. So will take some snooping to figure out.

figuring run time looks like it would be complicated so will have to go by water removed in a given time.

 

[MattT]

Just come in from putting a couple pans under drains to see what is happening. Did a quick google and all I found was from 5 to 20 gallons a day for central air. So will take some snooping to figure out.

figuring run time looks like it would be complicated so will have to go by water removed in a given time.

Those central units are gonna be in the 2 to 5 ton range. So those numbers are in the same ballpark range as my 4+ gallons per ton mini.

It certainly won't be easy to measure compressor runtime since both it and the fan are variable speed. I guess you could head outside with a stopwatch on a hot afternoon..................

 

[Kaizen]

Assuming these are in a larger space just open up the doors and see if it starts spitting out water. Might need some fans if it’s just a man door. Then if it works you know you need to chenge equipment or connect the rooms as said earlier


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[PoorOwner]

The minimum output on the Mitsubishi 24K 2 zone ODU is about 12K BTU.

So with 2 6000 BTU units running you have 6000 BTU each with no modulation, basically like having a 6000 BTU window AC.

12x12 is quite a small space, you reach target temp and won't have enough runtime to get the moisture out.

wait, is it 24k or 20k?

I have a 20k with a 15k+9k.. cooling 500 and 200 sq room

 

[kool55]

I was mistaken. Its a 20 K unit. Was thinking about leaving both room doors open to make it work harder/longer

 

[SALIV8]

Sounds like your system could have been sized for heating, and thus a bit oversized for cooling. I bet the 6ks are closer to 9k heating.

Making it work longer on low idu fan speed can only help, Imo.

 

[kool55]

OK guys, here is where I am at. You all seem to agree the system is to big for 12x12 rooms.This morning I left the doors open while on AC mode. Within 3-4 hours I had a constant condensate flow, verifying that the wall units are not in freon mode long enough.
I call the seller and try to get a customer service tech and was told they don't offer such . Instead they give me the Mitsubishi #. I call and talk to customer service. I tell them I can't get any condensation removal, etc. They say to get a licensed AC tech to size the room . They will not tell me that a 6K wall unit is to big for a 12x12 room. UNBELIEVABLE.
So I call the seller back and talk to a sales person who tells me the 6k wall unit is to big. Would have been nice to know that when I purchased it. 6K is Mitsubishi's smallest one.
Now I am going to heat the rooms to 75 degrees and then switch to Humidity mode. Reason being its hard to pull moisture out of the colder air. Will see if then it will produce condensate.

 

[PoorOwner]

Ok so it is 20K BTU outdoor unit, that's better than 24K. The lowest that compressor can go is about 6K BTU, so if you turn both indoor units on, fan speed low, set temp low, you should be able to get decent runtime with the compressor.

If not, you may want to look into a dehumidifier.

 

[kool55]

Think I did that but I will try again .Right now I heated rooms to 75 and now in dehumidify mode per salesman. Will check drain line later. Still can't believe Mitsubishi rep would not or could not tell me a 6K wall unit is too big for a 12x12 room.
Per salesman it seemed like the 6k wall unit was the issue more than the 20K Condenser unit. Since most if not all are inverter style now.

 

[fitter30]

Two evaporators 6 k and a 20k condenser is way oversized even with the compressor running at a low speed. Post 15 open the door or windows put some load on the unit and take temperature of the supply and return should be around 28* difference.

 

[PoorOwner]

You won't get much information out of Mitsubishi due to you are not a HVAC contractor.

Actually if you get a 6K or 9K indoor there is very little difference on those.

Normally when you buy a 9K or 6K single zone unit, they will go way low. The problem is that 20K compressor is still too large for the total area you are trying to cool.

I wouldn't go worry too much about the condensate. When the room is hot enough then it should make condensate. Sometimes I start my system early in the morning and i do not get condensate that day because the room never got hot enough.

But once you do get condensate I notice the moist coil seem to continue to make condensate continuously, as long as the compressor is running.


You should check if it is really uncomfortable for you or not.

 

[MattT]

Think I did that but I will try again .Right now I heated rooms to 75 and now in dehumidify mode per salesman. Will check drain line later. Still can't believe Mitsubishi rep would not or could not tell me a 6K wall unit is too big for a 12x12 room.
Per salesman it seemed like the 6k wall unit was the issue more than the 20K Condenser unit. Since most if not all are inverter style now.

Nobody can tell you for sure that 6K is oversized just from square footage. It's certainly a big red flag but Mitsu are correct in saying that it'll take a pro running numbers to 100% confirm what seems obvious.

I also think the salesman in wrong about the condenser. It's minimum is only low enough to run both heads at ~50%, or one wide open, which doesn't appear to be low enough for your lightly loaded heads.

 

[SALIV8]

OK guys, here is where I am at. You all seem to agree the system is to big for 12x12 rooms.This morning I left the doors open while on AC mode. Within 3-4 hours I had a constant condensate flow, verifying that the wall units are not in freon mode long enough.
I call the seller and try to get a customer service tech and was told they don't offer such . Instead they give me the Mitsubishi #. I call and talk to customer service. I tell them I can't get any condensation removal, etc. They say to get a licensed AC tech to size the room . They will not tell me that a 6K wall unit is to big for a 12x12 room. UNBELIEVABLE.
So I call the seller back and talk to a sales person who tells me the 6k wall unit is to big. Would have been nice to know that when I purchased it. 6K is Mitsubishi's smallest one.
Now I am going to heat the rooms to 75 degrees and then switch to Humidity mode. Reason being its hard to pull moisture out of the colder air. Will see if then it will produce condensate.

I have 5 room idu's that are oversized also. But they still work well. They are 9ks for about the same size rooms. Yup oversized. I would have loved the 6ks if Gree offered those.

Keep the doors opened, load up the units and you should be good if your odu can modulate low enough for the demand. I might even try a floor fan to circulate more so the idu sensors sense a load.

Do you have an 'I feel' mode on the remotes? My 'I feel' mode seems to be more accurate than the idu sensors for whatever reason.

 

[dsimatt]

What was the purpose of such a big condenser, are you planning on adding more head unit?

You might need to add in another head unit to add more load to the condensor and lower the 2 existing heads outputs.

 

[PsRumors]

Look up "Manual J" and run the numbers to see what size unit you need, it's a fairly simple process.

 

[brewchief]

I don't see a smaller dual zone condenser from Mitsubishi nor do they have heads smaller then 6k.
No easy solution that I can see.

I agree that you're probably oversized but it looks like you already have the smallest 2 zone combo Mitsubishi makes.

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[yeldogt]

It's a shame but there is a real lack of knowledge in the HVAC business ... and when it come to mini's .. less. Most guys have little experience with high efficiency VS products -- and mini's are high efficiency.

I have run into this knowledge void almost every time I have had a system installed

With multi head -- it's all about total load and how you are going to use the system. I have two 30k BTU systems (each with 3x12k heads). At one house two of the heads are slightly oversized -- but, both spaces have potential to need more cooling. One is a bedroom that we don't use all the time - so we need to be able to bump it up on demand. The other is a room with some heat gain in the summer and when we have parties we need more AC in that room as well. The other head is in a bedroom running all the time. So two of the heads are taking the minimum from the compressor -- remember with a multi (off is not off when some heads are running). I had to figure out what the minimums were for the loads .. sometimes a multihead is not what you want. But you also don't want three singles -- running at minimum levels either.

When you see efficiency ratings -- that's in the perfect range for that unit. A multi head properly sized running in the correct band is going to be more efficient vs a bunch of singles running out of the range.

Another benefit of the multi heads -- they can run above the rating a bit ... my memory is 110 percent.

The 6k units on the three head mitsubishi units are great as add ons -- I'm doing one in my current project for a tiny loft area. It's going in with an 18k for a kitchen and with a 12k or 9k for a walk out basement area. The mitsubishi engineers will tell you it's actually better when the total heads are greater than the output of the compressor.

This is why you need the total load of a building -- and understand that in most homes even on design days for AC -- do you really need the whole house at that temp? If the design temp in your area is 100 degrees outside -- how many days. Some people do the calculation at 70 degrees inside .. will the world end if you bump it up to 72 or even 74? My area is 102 -- we may hit that once every couple of years .. for a day. I never design for that -- and never notice any issues. I always size under ... I also keep my system on.

2x6k units on a 20k compressor -- was a mistake. 6k in a 12x12 kitchen will most likely be small ... in a windowless room with no heat gain .. it's way too big. It's all about the room -- and how its being operated. A basement space may require a fair amount of heat and almost no AC ..

It's no different vs how people talk about heater in garages. I maintain a temp -- so i want to use a standard design load. This is different when someone keeps a space at 40 wants to bring it up to 60.

 

[Jackfre]

Unless Mitsu had someone on the job they will not say anything about it, and you are not a certified dealer. Your system, for the space it is in, is grossly mismatched. If the specs say the parts can work together you have found the spot where they will not. I suspect the salesman looked in the manual and said, "Oh, yeah, Mitsu allows that." without an understanding of the space. By opening the doors you have proven that the system does work. You now need to create a single space out of it with through registers or fans to build the load and let one evap handle it. Not doing so is going to have that unit cycling and searching CONSTANTLY. Modulation is great, but you need that modulation to be able to create a "steady state" to adjust off. I will bet you dollars to donuts that a single 9000 would handle that space perfectly at a much higher efficiency, with communicating air.

 

[kool55]

Jackfre, I have come to that conclusion with the help of all of you. Thanks guys. Not expecting any help from EComfort who sold it to me. And really disappointed with the conversation with them.
So yesterday afternoon I had the temp set at 76 degrees with both rooms on dehumidify mode. This morning there was No condensate at all. So I turned off the tack room unit and set the feed room at 73 with ac and low speed with the door open.Wanted to see if it would make condensation with only 1 wall unit. 3 hours later I am getting 1 drip a second. Great!!
So now the plan is to install 2 thru the wall recirc. fans in the deviding wall. 1 high and 1 low in opposite directions. That will circulate air between the rooms while operating the 1 6K wall unit.
I have a small free standing dehumidifier the tack room since this morning and got the humidity down to 40 percent at 78 degrees[wall unit off]. Feels good. Not the way I wanted this project to go but I am at this point now. $3,600. later. Another learning experience.

 

[Jackfre]

I hope it works out for you. Hell of a situation.